Maser and Molecular Line Surveys of
Massive Star-forming Regions
Won-Ju Kim1 and Kee-Tae Kim2
Korea Astronomy and Space science Institute ( KASI )
1deneb@kasi.re.kr, 2 ktkim@kasi.re.kr
ABSTRACT
We made twice a simultaneous 22 GHz H2O and 44 GHz Class I CH3OH maser surveys of 103 ultra-compact HII regions (UCHIIs) in 2010 and 2011. We also performed a SiO (J=1-0, v=0) line survey of three
samples of massive star-forming regions in different evolutionary stages from 2010 to 2013: 134 infrared dark cores (IRDCs), 135 high-mass proto-stellar objects (HMPOs) and 103 UCHIIs . H2O and CH3OH
masers were detected in 70 (68%) and 48 (47%) UCHIIs, respectively. Among them, six H2O and twenty-four CH3OH masers are new detections. These high detection rates of both masers strongly suggest
that their occurrence periods are significantly overlapped with the UCHII phase. CH3OH masers always have smaller relative velocities than 10 km s−1 with respect to the ambient molecular gas, while H2O
masers frequently show larger relative velocities. Eighteen UCHIIs show H2O maser lines at relative velocities > 30 km s−1. The occurrence and disappearance of H2O masers are frequent over one-year
time interval. In contrast, CH3OH masers rarely show significant variation in peak velocity, peak intensity, and line shape. The isotropic luminosities of both masers well correlate with the bolometric
luminosities of the central stars in the case that data points of low- and intermediate-mass proto-stars are added. They also tend to increase with the 2/6 cm radio continuum luminosities of UCHIIs and the
850 µm continuum luminosity of the parent dense cores. SiO thermal emission was detected in 52 IRDCs (39 %), 22 HMPOs (16 %), and 24 UCHIIs (23 %). Almost SiO emission–detected UCHIIs (96%) have
H2O and/or CH3OH maser emissions. SiO luminosity is proportional to bolometric luminosity and maser (H2O and CH3OH) luminosities. LSiO/Lbol ratio tend to decrease as central (proto)stars evolved.
INTRODUCTION
OBSERVATION
The processes of massive star-forming are poorly understood unlike formation of low-mass star. It is known
that the evolution of massive star-forming starts in an infrared dark cloud (IRDC) and then IR emissions are
emitted from central condensation region in hot core, which is high-mass proto-stellar object (HMPO). The
proto-stellar object eventually reaches main-sequence and forms HII region around central star, which
becomes ultra-compact HII region (UCHII). The powerful outflow is important in star formation and generally
discovers in IRDC, HMPO and UCHII. H2O and CH3OH masers with SiO thermal emission are useful tracer of
shock by outflow. H2O and CH3OH masers are excited by collisional pumping. H2O maser are produced in more
dense and hot regions than formation regions of CH3OH. SiO is formed in shocked regions like Si is released
from dust grain and conjoin with O (Schilke et al. 1997; Caselli et al. 1997). Si in interstellar medium is
observable for ~ 104 yr (Pineau des Forets et al. 1997), therefore SiO indicates recent shock activity. We will
interpret the evolutionary sequence of massive star-forming by means of H2O, CH3OH masers and SiO thermal
emission.
H2O & CH3OH Observation
SiO thermal Observation
Sources
103 UCHIIs
134 IRDCs, 135 HMPOs, 103 UCHIIs
Telescope
KVN Yonsei 21m
KVN Yonsei/Ulsan/Tamna 21m
Transition
H2O, 616-523 ( 22.23508GHz )
CH3OH, 70-61 A+ ( 44.06943GHz )
SiO, v=0, J=1-0 ( 43.423853GHz )
Beam size
130’’ @ 22GHz, 65’’@44GHz
64’’@43GHz
RMS
0.5Jy
30mK
Velocity resolution
0.21 km s-1
1.7 km s-1
※ UCHII : WC89 and KCW94, HMPO : Sridharan et al. (2002) and Zhang et al. (2005), IRDC : Chambers et al. (2009)
RESULTS & DISCUSSION 2: SiO (v=0, J=1-0) thermal emission
RESULTS & DISCUSSION 1: H2O & CH3OH masers
Detection Rates
Detection Rates & SiO emission
Detection rates of H2O and CH3OH for UCHIIs are sufficient
high values. The detection rate of H2O is similar with
previous H2O surveys’s rates. So far, Class I CH3OH
masers in previous surveys have been observed toward
younger stages than UCHIIs. However, we detected
enough CH3OH masers toward UCHIIs. It is seen that
occurrence period of Class I CH3OH maser considerably
overlap with UCHII phase.
1.0
3.5
(a)
3.0
0.8
100
12
0.4
VCH3OH - Vsys (km s-1)
VH2O - Vsys (km s-1)
-50
0
-150
-100
-50
0
50
Vsys (km s-1)
100
150
-100
-50
10
0
50
Vsys (km s-1)
100
150
10-2
10-2
LH2O (L O• )
LH2O (L O• )
LH2O (L O• )
10
10-6
IRDC
HMPO
Maser / SiO sources
IRDC (52)
HMPO (22)
UCHII (24)
H2O / SiO
30/52
15/22
22/24
CH3OH / SiO
39/52
19/22
22/24
●, ○ UCHII
10-5
10-7
10-2
-8
10
-6
(a)
UCHII
HMPO
IRDC
(b)
Average
Median
10
10
10-6
10-5
10-6
10-5
10-8
10-6
10-10
100
10-7
-7
10
102
10-7
10-8
102
104
Lbol (L O• )
106
10
108
H2O and CH3OH maser luminosities
are well related with bolometric
luminosity for low- (LMYSOs,
Furuya et al. 2003) and
intermediate-mass YSOs (IMYSOs,
Bae et al. 2011) with UCHIIs.
: LH2O = 3.98× 10-9 (Lbol)0.70 with
ρH2O = 0.90
: LCH3OH = 7.44 × 10-9(Lbol)0.57 with
ρCH3OH = 0.77
10
11
10
L2cm (mJy pc2)
12
10
8
13
10
10
2cm radio continuum luminosity is
proportional to LH2O and LCH3OH
: LH2O = 4.36× 10-10 (L2cm)0.46 with
ρH2O = 0.52
: LCH3OH = 2.18 × 10-11(L2cm)0.51 with
ρCH3OH = 0.74
The radio continuum emission of
UCHIIs is mainly originated from
HII region around central stars
although a part of those comes
from radio jets of UCHIIs.
LMaser vs. L6cm
100
10
10
-3
10
10-2
●, ○ UCHII
□,
△, ◇ IMYSO
-4
10
LCH3OH (L O• )
10-4
10-6
10-8
10-5
10-6
-7
10
10-10
-8
10
106
108
1010
L6cm (mJy pc2)
10
10
L850µm (Jy pc2)
10
10
LH2O and LCH3OH are proportional to
L850µm driven by surrounding dust
emission.
: LH2O = 2.49× 10-11 (L850µm)0.61 with
ρH2O = 0.35
: LCH3OH = 1.72 × 10-16(L850µm)1.08 with
ρCH3OH = 0.76.
We guess that massive stars made
by massive molecular cores are
able to produce bright Lbol and then
induce bright maser luminosities.
1012
1014
10-8
10-6
10-4
LH2O (L O• )
10-2
In the case of LMYOs, LH2O is well associated with radio continuum
driven by ionized jets or outflows. On the other hand, the radio
continuum of UCHIIs is mostly originated from HII region around central
stars although a portion of those are induced by radio jets of UCHIIs.
In UCHIIs, H2O maser luminosity
is higher than CH3OH maser
luminosity.: 10-7.5 ≤ LH2O/L⊙ ≤ 10-1.5
and 10-7.5 ≤ LCH3OH/L⊙ ≤ 10-3.5.
A relation between LH2O and
LCH3OH for UCHIIs shows bad
correlation. However, a fitted
result of UCHIIs with IMYSOs
shows improved a relation.
: LCH3OH = 9.97 × 10-4(LH2O)0.47 with
ρ = 0.62.
It is seen to relate with outflows
activity. We also find out that
massive central stars produce
luminous maser emissions.
SUMMARY
1. H2O maser emission was detected in 70 (68%) UCHIIs and CH3OH maser emission in 48 (47%) UCHIIs.
Among then, 15 H2O maser sources and 33 CH3OH maser sources are new detection.
2. CH3OH masers always have small ( < 10km s-1 ) relative velocities, while H2O masers commonly have
broader relative velocities with respect to the ambient dense molecular gas.
3. The isotropic luminosities of both masers tend to increase with the bolometric luminosity of central star
: LH2O = 3.98× 10-9 (Lbol)0.70 with ρH2O = 0.90 and LCH3OH = 7.44 × 10-9(Lbol)0.57 with ρCH3OH = 0.77.
4. SiO thermal emission was detected in 52 IRDCs (39 %), 22 HMPOs (16 %), and 24 UCHIIs (23 %).
Almost SiO emission–detected UCHIIs (96%) have H2O and/or CH3OH maser emissions.
5. Integrated intensity and FWHM of SiO emissions tend to increase with evolutionary sequences.
6. The more luminous SiO sources are associated with higher bolometric luminosity. LSiO/Lbol ratio tend to
decrease as central (proto)stars evolved.
7. LSiO and SiO column density are related with LH2O and LCH3OH maser luminosities.
104
Lbol (L O• )
106
-12
108
IRDC
HMPO
UCHII
(a) shows to compare Lbol with SiO emission luminosity. LSiO of HMPOs and UCHIIs are well associated with
Lbol while LSiO of IRDC is less correlated with Lbol: UCHII, LSiO = 3.56× 10-12 (Lbol)1.18 with ρSiO = 0.77; HMPO, LSiO
= 1.23× 10-09 (Lbol)0.83 with ρSiO = 0.93; IRDC, LSiO = 1.31× 10-06 (Lbol)0.21 with ρSiO = 0.39. We find out that more
luminous SiO sources are associated with higher bolometric luminosity (Codella et al. 1999). We also find that
younger stages have more intense SiO emission then consider identical Lbol. (b) presents LSiO / Lbol ratio for
different evolutionary stages. Like (a), more young stages have higher LSiO/Lbol ratio than more old stages
(Lopez-Sepulcre et al. 2011).
11
LH2O vs. LCH3OH
●, ○ UCHII
◼, ▲ LMYSO
104
9
Comparison of SiO properties and Maser luminosities
10-4
(a)
10-4
-6
10
UCHII
LSiO = 5.28(LH2O)0.96 with ρSiO = 0.50
LSiO = 2.33 (LCH3OH)1.04 with ρSiO = 0.93
UCHII
HMPO
IRDC
UCHII
HMPO
IRDC
UCHII
HMPO
IRDC
< LSiO vs. Lmaser >
10-2
10-2
10-2
LH2O (L O• )
100
9
(b)
10-4
10-6
HMPO
LSiO = 3.42(LH2O)0.70 with ρSiO = 0.68
LSiO = 0.13 (LCH3OH)0.86 with ρSiO = 0.89
(c)
IRDC
LSiO = 3.39×10-4(LH2O)0.62 with ρSiO = 0.33
LSiO = 8.20×10-5 (LCH3OH)0.90 with ρSiO = 0.49
< N(SiO) vs. Lmaser >
10-6
All
NSiO = 1.58×10-36(LH2O)2.31 with ρSiO = 0.51
NSiO = 1.37×10-43 (LCH3OH)2.75 with ρSiO = 0.43
10-8
UCHII
10-8
10-8
10-10
10-2
10-2
UCHII
HMPO
IRDC
10-4
10-4
10-6
LCH3OH (L O• )
10-2
8
LH2O (L O• )
10
LCH3OH (L O• )
-8
-10
LH2O (L O• )
-5
10-6
-8
10-8
NSiO = 4.24×10-24(LH2O)1.45 with ρSiO = 0.32
NSiO = 3.14×10-26 (LCH3OH)1.55 with ρSiO = 0.60
HMPO
10-2
UCHII
HMPO
IRDC
10-4
10-6
LCH3OH (L O• )
LCH3OH (L O• )
10
LCH3OH (L O• )
10-4
-4
10-4
Log(LSiO/Lbol)
LSiO ( L O• )
10-3
-4
LCH3OH (L O• )
UCHII
10-8
10-3
LH2O (L O• )
HMPO
Comparison of SiO thermal Luminosity and Central star properties
10
-10
IRDC
UCHII
In the case of UCHII, the majority (92%) of SiO-detected sources have H2O or/and CH3OH masers. In IRDC,
although SiO detection rate is the highest among evolutionary stages, H2O (58%) and CH3OH (75%) masers
detections for SiO-detected sources are less than other stages. The detection rate increases up to 50 % for
the 18 UCHIIs with high-velocity H2O masers. However, the SiO emissions were not detected toward four
blue-dominant H2O sources ( V > 50 km s-1 ) of UCHIIs.
10-6
-8
UCHII
Masers Detection Rates for SiO detected sources
10-4
-4
HMPO
(a) shows detection rates of SiO emission toward IRDC (52/134=39%), HMPO (22/135=16%) and UCHII
(24/103=23%). Detection rate of IRDC is the highest and then rate decrease to HMPO. Again, detection rate
increase slight to UCHIIs. It is seen that young stage like IRDCs has young SiO outflow because SiO emission
has short lifetime of ~ 104 years. (b), (c) Integrated intensity and FWHM increase slight as central (proto) stars
evolve. We do not know whether the SiO emission of UCHIIs indicates recently produced young outflow or the
remainder of old outflow or other factors like cloud-cloud collisions.
10-3
10-4
10
8
4
0.0
IRDC
●, ○ UCHII
●, ○ UCHII
□,
△, ◇ IMYSO
◼, ▲ LMYSO
10-6
10
6
0.0
Comparison of Maser Luminosity and Central star properties
-2
1.5
0.2
H2O masers show a broad velocity distribution while all
CH3OH masers are located within ± 10 km s-1. Usually, H2O
are produced in shock region by high-velocity outflow or jet
while CH3OH are made in interaction region between lowvelocity outflow and ambient gas. The H2O maser shows
blue-shifted pattern. The vast majority of the strongest H2O
components (91%) are particularly within 20 km s-1.
However, four sources of strongest H2O components have
high relative velocity, which are possible to trace highvelocity jet or outflow. According to the theoretical models,
low relative velocity of CH3OH is because it is destroyed in
fast shock over 10 km s-1.
-5
-100
2.0
1.0
Maser velocities
5
0
FWHM ( km s-1 )
Area ( K km s-1 )
Detection Rate
0.6
0.5
Strongest CH3OH coomp.
CH3OH comp.
50
(c)
Average
Median
2.5
※ WC89 : Wood & Churchwell 1989, KCW94 : Kurtz et al. 1994
Strongest H2O coomp.
H2O comp.
14
(b)
Average
Median
10-8
NSiO = 1.73×10-16(LH2O)0.80 with ρSiO = 0.25
NSiO = 6.17×10-10(LCH3OH)0.28 with ρSiO = 0.07
UCHII
HMPO
IRDC
IRDC
NSiO = 1.76×10-19(LH2O)0.93 with ρSiO = 0.32
NSiO = 6.38×10-25(LCH3OH)1.19 with ρSiO = 0.41
< X(SiO) vs. Lmaser >
10-6
All
XSiO = 7.32×10-24(LH2O)-1.83 with ρSiO = -0.57
XSiO = 1.98×10-34 (LCH3OH)-2.80 with ρSiO = -0.60
10-8
UCHII
XSiO = 3.20×10-5(LH2O)-0.03 with ρSiO = -0.01
XSiO = 1.97×106 (LCH3OH)1.16 with ρSiO = 0.56
10-10
10-10
10-10
HMPO
XSiO = 2.17×10-7(LH2O)-0.13 with ρSiO = -0.07
XSiO = 1.90×10-4 (LCH3OH)0.16 with ρSiO = 0.12
10-12
-9
10
10
-8
10
-7
-6
-5
10
10
LSiO ( L O• )
10
-4
-3
10
10-12
1012
10-12
1013
N(SiO) ( cm-2 )
1014
10-11
10-10
X(SiO)
10-9
10-8
IRDC
XSiO = 1.51×10-23(LH2O)-1.75 with ρSiO = -0.42
XSiO = 2.17×10-13 (LCH3OH)-0.41 with ρSiO = -0.11
(a), (b) and (c) plot data points of UCHIIs, HMPOs and IRDCs for LSiO against Lmaser. For (a), LH2O and LCH3OH
are proportional to LSiO. LCH3OH is markedly related with LSiO. We guess that is because SiO and CH3OH are
produced in interaction region between outflow and ambient gas (Garay et al. 2002). SiO and CH3OH are
known as tracer of outflow however the SiO emission indicates recently created outflow. We do not know
yet whether SiO and CH3OH indicate identical activity like recently created outflow. For (b), SiO column
density also shows similar pattern with Lsio but correlation diminish. For (c), SiO abundance do not show
different tendency unlike (a) and (b). We guess that our NH2 data are affected from central star contribution
like bolometric luminosity. In the case of NH2 of IRDCs, we did not reproduce NH2 and just brought data of
Sanhueza et al. 2012. Therefore, we have to reproduce NH2 of IRDCs and to apply new NH2 to (c) figures.
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